The HeLa cell line is the oldest, most widely distributed, permanent human cell line. As a nearly ubiquitous inhabitant of laboratories using tissue culture techniques, its aggressive growth characteristics make it a problematic contaminant that can overgrow less robust cell lines. Consequently, HeLa contamination is common in both the research laboratory and cell line repository contexts, and ...

Long interspersed elements 1 (L1) are active mobile elements that constitute almost 17% of the human genome. They amplify through a "copy-and-paste" mechanism termed retrotransposition, and de novo insertions related to these elements have been reported to cause 0.2% of genetic diseases. Our previous data demonstrated that the endonuclease complex ERCC1-XPF, which cleaves a 3' DNA flap structur...

Expression of the L1 retrotransposon can damage the genome through insertional mutagenesis and the generation of DNA double-strand breaks (DSBs). The majority of L1 loci in the human genome are 5'-truncated and therefore incapable of retrotransposition. While thousands of full-length L1 loci remain, most are retrotranspositionally-incompetent due to inactivating mutations. However, mutations le...

L1 is the most proliferative autonomous retroelement that comprises about 20% of mammalian genomes. Why L1s have proliferated so extensively in mammalian genomes is an important yet unsolved question. L1 copies are amplified via retrotransposition, in which the DNA cleavage specificity by the L1-encoded endonuclease (EN) primarily dictates sites of insertion. Whereas mammalian L1s show target p...

Human L1 elements are highly abundant poly(A) (non-LTR) retrotransposons whose second open reading frame (ORF2) encodes a reverse transcriptase (RT). We have identified an endonuclease (EN) domain at the L1 ORF2 N-terminus that is highly conserved among poly(A) retrotransposons and resembles the apurinic/apyrimidinic (AP) endonucleases. Purified L1 EN protein (L1 ENp) makes 5'-PO4, 3'-OH nicks ...

Retrotransposition of human LINE-1 (L1) element, a major representative non-LTR retrotransposon in the human genome, is known to be a source of insertional mutagenesis. However, nothing is known about effects of L1 retrotransposition on cell growth and differentiation. To investigate the potential for such biological effects and the impact that human L1 retrotransposition has upon cancer cell g...

Long interspersed nuclear element-1 (L1) retrotransposons are normally suppressed in somatic tissues mainly by DNA methylation and antiviral defense. However, L1s can be desuppressed in cancers to act as insertional mutagens and cause genomic instability by creating DNA double strand breaks and chromosomal rearrangements. Whereas the frequency of somatic L1 insertions varies greatly among indiv...

The Long interspersed element 1 (LINE1 or L1) retrotransposon constitutes 17% of the human genome. There are currently 80-100 human L1 elements that are thought to be active in any diploid human genome. These elements can mobilize into new locations of the genome, resulting in changes in genomic information. Active L1s are thus considered to be a type of endogenous mutagen, and L1 insertions ca...

The Alu family is a highly successful group of non-LTR retrotransposons ubiquitously found in primate genomes. Similar to the L1 retrotransposon family, Alu elements integrate primarily through an endonuclease-dependent mechanism termed target site-primed reverse transcription (TPRT). Recent studies have suggested that, in addition to TPRT, L1 elements occasionally utilize an alternative endonu...